Perfect Game runs the WWBA in East Cobb. They use the rosters, which include contact information, to later solicit participation at PG events, such as the Mid-Atlantic Underclass. So yes, they are mass-mailed and, I suspect, go out to many hundreds, if not several thousand, "prospects."
That said, it is possible that PG found your son by seeing him play or through a college coach, pro scout, or area HS or travel coach. You just don't know.
PG is the best of the showcase/prospect organizations out there. Yes, they are expensive, but if a player can stand out at PG showcase, he will get some looks. Keep in mind, however, the numbers at these showcases.
If you are concerned, talk to your son's coach and see what he thinks. The Underclass events are the stepping stones to later PG events (Top Prospect events), and your son's coach may have some insight on whether you should take these steps.
Some standouts don't need this sort of showcase help. The majority of kids do. And the PG events are top-notch events.